After reading a lot of different articles on the Internet I'm still confused about how to find exactly what is using my memory.

After upgrading to Ubuntu Server 21.10 from 20.04 my memory usage increased dramatically and I'm trying to find out what is responsible for that.

When I'm logging into the server there are some welcome stats that say: Memory usage: 65%.

When I run free -m I get:

               total        used        free      shared  buff/cache   available

Mem:           31881       20575        9669         162        1636       10680

Swap:           8191           0        8191

So far it matches. I understand that there is some confusion here and my actual free memory is free + buff/cache or something like that but then I found a command on the Internet that returns the sum of memory consumption of all processes:

$ echo $(ps -o rss= ax | tr '

' +) 0 | bc

5978056

That gives 5-6GB. It doesn't match with any value returned from free -m. The result of top sorted by memory column seems to confirm this:

top - 10:53:49 up 3 days, 13:28,  1 user,  load average: 0.11, 0.10, 0.09

Tasks: 451 total,   1 running, 438 sleeping,   0 stopped,  12 zombie

%Cpu(s):  0.2 us,  0.1 sy,  0.0 ni, 99.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st

MiB Mem :  31881.4 total,   9791.5 free,  20453.8 used,   1636.1 buff/cache

MiB Swap:   8192.0 total,   8192.0 free,      0.0 used.  10801.7 avail Mem



    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND

   3930 mssql     20   0   20.6g   1.1g  44584 S   2.0   3.4 116:22.67 sqlservr

   3115 mysql     20   0 5336868 726652  19148 S   0.3   2.2  11:29.69 mariadbd

  19021 www-data  20   0  438324 231656 169396 S   0.0   0.7   3:31.67 php-fpm8.0

   3348 www-data  20   0  438112 231096 171232 S   0.0   0.7   3:52.81 php-fpm8.0

   3349 www-data  20   0  436832 227820 168664 S   0.0   0.7   3:26.81 php-fpm8.0

   3356 www-data  20   0  429292 223864 171360 S   0.0   0.7   3:59.62 php-fpm8.0

   3354 www-data  20   0  427580 221492 170016 S   0.0   0.7   3:47.99 php-fpm8.0

   3357 www-data  20   0  428052 221336 169144 S   0.0   0.7   3:51.86 php-fpm8.0

   3355 www-data  20   0  427056 220772 170064 S   0.0   0.7   3:35.60 php-fpm8.0

   3345 www-data  20   0  427080 220116 169212 S   0.0   0.7   3:51.67 php-fpm8.0

   3365 www-data  20   0  425712 220024 171216 S   0.0   0.7   3:42.05 php-fpm8.0

  19700 www-data  20   0  424868 218940 169908 S   0.0   0.7   3:39.68 php-fpm8.0

   3363 www-data  20   0  423260 218804 171252 S   0.0   0.7   3:45.00 php-fpm8.0

   3341 www-data  20   0  423184 217468 170044 S   0.0   0.7   3:49.10 php-fpm8.0

   3353 www-data  20   0  421016 214860 169556 S   0.0   0.7   3:30.55 php-fpm8.0

   3351 www-data  20   0  420432 212680 169256 S   0.0   0.7   3:25.20 php-fpm8.0

   2674 www-data  20   0   22.7g 169652  41068 S   0.0   0.5   3:03.73 dotnet

   2696 git       20   0 2181008 165396  43788 S   0.0   0.5   7:55.15 gitea

   1324 root      19  -1  134508  72360  71296 S   0.0   0.2   0:15.71 systemd-journal

   4159 root      20   0 2052028  62724  31824 S   0.0   0.2   4:02.05 dockerd

2289460 root      20   0 1910052  39892  20176 S   0.0   0.1   0:23.22 snapd

   2726 root      20   0 2011284  31740  16344 S   0.0   0.1   8:44.13 containerd

   2703 root      20   0  270968  26244  19164 S   0.0   0.1   0:23.63 php-fpm8.0

   3251 www-data  20   0  102500  21180  16652 S   0.0   0.1   6:46.80 nginx

   2734 root      20   0 1139124  20408   7864 S   0.3   0.1  14:21.22 fail2ban-server

   3254 www-data  20   0  101948  20048  16336 S   0.0   0.1   0:02.27 nginx

   4165 minidlna  20   0  239012  19372  14324 S   0.0   0.1   0:39.26 minidlnad

   2017 root      rt   0  280960  18584   8772 S   0.3   0.1   0:47.47 multipathd

   2801 root      20   0  112464  18560   9988 S   0.0   0.1   0:00.05 unattended-upgr

   4242 root      20   0   84880  17604  14660 S   0.0   0.1   0:15.41 smbd

   2664 root      20   0   34740  17488   8508 S   0.0   0.1   0:00.08 networkd-dispat

   3253 www-data  20   0  101372  17020  13748 S   0.0   0.1   0:00.18 nginx

 203855 root      20   0  295244  16160  13364 S   0.0   0.0   0:02.36 packagekitd

   2700 mssql     20   0   72632  14852   6224 S   0.0   0.0   0:00.85 sqlservr

   3257 www-data  20   0  101240  14756  11540 S   0.0   0.0   0:00.02 nginx

   4234 root      20   0   22436  12928   3544 S   0.0   0.0   0:10.19 ddclient - slee

   4160 root      20   0   70756  12212   9912 S   0.0   0.0   0:09.06 nmbd

   2676 root      20   0  395152  11632   8612 S   0.0   0.0   0:53.73 udisksd

   2591 systemd+  20   0   23640  11164   7108 S   0.0   0.0   1:26.88 systemd-resolve

      1 root      20   0  166644  10784   5516 S   0.0   0.0   0:29.92 systemd

   4561 root      20   0   26968  10156   7144 S   0.0   0.0   0:44.81 portainer

   4288 root      20   0   84864   9184   6240 S   0.0   0.0   0:00.99 lpqd

1319978 rychu     20   0   15832   8848   6896 S   0.0   0.0   0:00.06 systemd

   4284 root      20   0   82640   8748   5956 S   0.0   0.0   0:00.59 smbd-notifyd

   3255 www-data  20   0  101088   8668   5496 S   0.0   0.0   0:00.00 nginx

   2706 redis     20   0   70552   8420   6348 S   0.0   0.0  13:27.82 redis-server

1319928 root      20   0   14860   8112   6648 S   0.0   0.0   0:00.03 sshd

   2671 root      20   0  126992   7576   6720 S   0.0   0.0   0:22.24 thermald

Here is my snap list output:

$ snap list

Name                 Version    Rev    Tracking       Publisher   Notes

canonical-livepatch  10.1.2     126    latest/stable  canonical✓  -

core                 16-2.54.3  12725  latest/stable  canonical✓  core

core18               20211215   2284   latest/stable  canonical✓  base

core20               20220114   1328   latest/stable  canonical✓  base

lxd                  4.0.8      21835  4.0/stable/…   canonical✓  -

So I'm confused where does my ~14GB of used memory is?